The present invention relates generally to an expansion anchor, and more particularly to an expansion anchor for anchoring in a hole formed in a support structure.
An expansion anchor for anchoring in drill-holes is adapted preferably for anchoring in drill-holes that have been prepared such that they have undercut portions which flare inwards.
Expansion anchors for securing an object to a support structure of the type under discussion, which comprise an expansion member supported at the bottom of the drill hole and an expander cone onto which an expansion sleeve is driven, have been known and are disclosed, for example in applicant's U.S. Pat. Nos. 3,733,959; 3,340,761; 3,955,464; 3,964,229; 3,471,183; 3,802,059; 4,028,857, etc.
Expansion anchors of the foregoing type are used in particular in ceilings, because by driving the expansible sleeve onto the expander cone of the expansion member, resting on the bottom of the drill-hole, an anchorage, that is not liable to develop cracks, is achieved. The load applied to the expansion member ensures that expansion will increase if the drill-hole becomes widened as a consequence of a crack running through the bore; this increase in expansion compensates for the loss in a pull-out force, caused by the bore opening up, or at least substantially reduces this loss.
In order, firstly, to reduce the amount of energy required to drive the expansible sleeve, and, secondly, to increase the expansion ability, it is advantageous with the expansion anchor of this kind to provide the drill-hole with an undercut that widens towards the bottom of the drill-hole. With known expansion anchors of this type, a stay bolt, having a pressed-on expander cone, is generally used as the expansion member. The thread of the stay bolt serves for fastening objects or for screwing in extension pieces, on which objects may be suspended by means of wires, perforated bands or similar means. The manufacture of the stay bolts, and especially of the extension pieces, is extremely expensive and, in view of the shallow anchoring depth that is desired, these components are too large on account of the manufacturing method.